British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Guns, torpedoes, mines, bombs, missiles, ammunition, fire control, radars, and electronic warfare.
Byron Angel
Senior Member
Posts: 1655
Joined: Sun Mar 06, 2011 1:06 am

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by Byron Angel »

dunmunro wrote: Wed May 12, 2021 7:53 pm
Byron Angel wrote: Wed May 12, 2021 6:09 pm
dunmunro wrote: Wed May 12, 2021 9:07 am It not possible to add ~4 tons at the director level (~55ft AWL) and not have it cause serious issues for ship stability. As the BuOrd history makes clear, one of the design goals of Mk37 was to reduce topweight, and this goal was not met.

Hi dunmunro,
Apparently, Bureau of Ships did not share your concerns.

B
Really, so the fact that the pre-Fletcher Mk37 equipped destroyers all came out seriously top heavy and overweight, forcing a reduction in armament, was not true?

I recommend that you consult Friedman’s “U.S. Destroyers - an Illustrated Design History” and John C Reilly’s “United States Navy Destroyers of World War II”.

B
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by wmh829386 »

The problem with discussing the effectiveness of WW2 long range AA system always ran into the problem of unreliable kill claims and complicated technical details.

Perhaps I should put forward my assertion first.
1. Mk 37/ Mk 1 GFCS is significantly more effective than HACS this is especially true after Mk37 receives radar that could lobe switch along train & elevation, allowing blind fire.
(The HACS has far too many fundermental weaknesses: incapable to deal with elevation changes, distorted representation for low elevation targets by HACT, insufficient rigidity of director, and use of maximum strength for its Type 285 to find height.)

2. Despite Mk 37/ Mk 1 relative effectiveness, its effectiveness and efficiency is still questionable compared to medium and short range weapons when one considers the effect of shell travel time at long range and FC saturation.
(Destroyer with a single long range director will almost be useless in a self defence situation against a squadron of 6 dive bombers. As simply breaking into two flights with contant change in course and Altitude (above 10k ft) would bring most DB right above the destroyer with one flight of 3 unmolested. Alternatively 6 TB that decided to make a cross drop pose an easier but similar problem. Even CL with 2 Mk 37 don't fair much better it can deal with 2 flights and not more )

3. The USN eventually mount more and more short range gyro directors as the problem of FC saturation becomes apparent, allowing 5"/38 with VT fuze to switch to local control. VT fuse also makes engaging dive bomber a bit more feasible as not FC could deal with accelerating target, fuse time will almost always be incorrect. Ultimately it makes 5"/38 even more effective but it also marks the faliure of pre-war concept of long range AA that Mk 37 & HACS are designed for (that they could turn away/ breakup group of attackers before they drop their ammunition, in reality, splitting of flights and defensive flying breech the long range barage again and again)

As for the guns themselfs, 4.5" have better range and shell travel time at range with slightly less projectile weight (23 kg instead of 25 kg) but the 4.5" uses fix ammunition (shell with brass together) for most mount, which lowered ROF.
User avatar
OSCSSW
Junior Member
Posts: 13
Joined: Sun Sep 26, 2021 2:47 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by OSCSSW »

BZ (well done) wmh829386.
Very informative and concisely presented case. Unlike some of the others above, not a hint of petulance, condescension and preaching. Keep up the good work.
wmh829386 wrote: Tue Oct 05, 2021 3:22 am The problem with discussing the effectiveness of WW2 long range AA system always ran into the problem of unreliable kill claims and complicated technical details.

Perhaps I should put forward my assertion first.
1. Mk 37/ Mk 1 GFCS is significantly more effective than HACS this is especially true after Mk37 receives radar that could lobe switch along train & elevation, allowing blind fire.
(The HACS has far too many fundermental weaknesses: incapable to deal with elevation changes, distorted representation for low elevation targets by HACT, insufficient rigidity of director, and use of maximum strength for its Type 285 to find height.)

2. Despite Mk 37/ Mk 1 relative effectiveness, its effectiveness and efficiency is still questionable compared to medium and short range weapons when one considers the effect of shell travel time at long range and FC saturation.
(Destroyer with a single long range director will almost be useless in a self defence situation against a squadron of 6 dive bombers. As simply breaking into two flights with contant change in course and Altitude (above 10k ft) would bring most DB right above the destroyer with one flight of 3 unmolested. Alternatively 6 TB that decided to make a cross drop pose an easier but similar problem. Even CL with 2 Mk 37 don't fair much better it can deal with 2 flights and not more )

3. The USN eventually mount more and more short range gyro directors as the problem of FC saturation becomes apparent, allowing 5"/38 with VT fuze to switch to local control. VT fuse also makes engaging dive bomber a bit more feasible as not FC could deal with accelerating target, fuse time will almost always be incorrect. Ultimately it makes 5"/38 even more effective but it also marks the faliure of pre-war concept of long range AA that Mk 37 & HACS are designed for (that they could turn away/ breakup group of attackers before they drop their ammunition, in reality, splitting of flights and defensive flying breech the long range barage again and again)

As for the guns themselfs, 4.5" have better range and shell travel time at range with slightly less projectile weight (23 kg instead of 25 kg) but the 4.5" uses fix ammunition (shell with brass together) for most mount, which lowered ROF.
"You see those battleships sitting there, and you think they float on the water, don't you?... You are wrong, they are carried to sea on the backs of those Chief Petty Officers!" Admiral William Halsey USN :wink:
Steve Crandell
Senior Member
Posts: 954
Joined: Wed Feb 05, 2014 7:05 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by Steve Crandell »

People often quote rounds/kill to disparage the 5"/38. I don't think that is a very meaningful statistic, and this is why:

A force armed with 4.5" AAA is attacked by aircraft. 100 rounds are expended and one aircraft is shot down. 100/1 = 100 rpk.

Another force armed with 5"/38 AAA is attacked by aircraft. 500 rounds are expended and two aircraft are shot down. 500/2 = 250 rpk.

If you only look at rpk, the 4.5" is clearly better, but which weapon type was actually more effective? One shot down one aircraft, and the other shot down two. If you had plenty of ammunition because of fleet weapon standardization and your ships also just carried more per gun, you would be more likely to just fire as many rounds as possible, and your rpk would tend to be worse.
Byron Angel
Senior Member
Posts: 1655
Joined: Sun Mar 06, 2011 1:06 am

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by Byron Angel »

Well presented; my compliments, wmh829386.

FWIW, here are some reference resources I found useful in seeking to better understand the HACS fire control system and its relationship to RN LR HAA.

“The Royal Navy 1930-2000, Innovation and Defence”; Richard Harding (ed); Taylor & Francis, 2005.
> Chapter 1 - Managing the Aerial Threat, by Philip Pugh
- - -
“The Applications of Radar and Other Electronic Systems in the Royal Navy in World War 2”; F A Kingsley (ed); Naval Radar Trust, 1995.
> Monograph 1 – Weapon Direction in the Royal Navy, 1935-145, by H W Pout.
> Monograph 2 – Weapon Control in the Royal Navy, 1935-45, by H W Pout.:
Section 1 – Weapon Radar Development
Section 2 – Weapon Systems and Their Performance.
- - -
“From Fellside to Flyplane – How a very junior officer changed the whole course of RN Anti-Aircraft fire control despite strong Admiralty opposition – Iville Porteous, Commissioned Ordnance Officer, A Career in Naval Gunnery 1921-1952”, by Commander Roger Porteous RN.; privately published, 2020.


The RN’s wartime LR HAA saga is a very involved and sad story that stretches far beyond the basic shortcomings of the HACS design alone.

Re the Mk37 GFCS - it is worthy of note that not until the last quarter of 1942 did even one-half of the USN’s operational warships in the PTO carry the Mk37 GFCS. The other USN ships serving in the Pacific were still fitted with MK19, Mk28 and Mk33 FC systems for LR HAA control.

Byron
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by dunmunro »

wmh829386 wrote: Tue Oct 05, 2021 3:22 am

Perhaps I should put forward my assertion first.
1. Mk 37/ Mk 1 GFCS is significantly more effective than HACS this is especially true after Mk37 receives radar that could lobe switch along train & elevation, allowing blind fire.
(The HACS has far too many fundermental weaknesses: incapable to deal with elevation changes, distorted representation for low elevation targets by HACT, insufficient rigidity of director, and use of maximum strength for its Type 285 to find height.)
You'll have to support the 1st sentence with some operational proof. In practise, in 1942, Mk33/37 was not effective.

HACS could deal with elevation changes as could any predictive FC system but it could not predict target location based upon a constant rate of altitude change however, in practise, no system could do that effectively because targets didn't change altitude at a constant rate - aircraft nearly always change their rate of motion when changing altitude.

The HACT had various work arounds for long range low altitude targets. HADTs didn't suffer from lack of rigidity. Type 285 didn't find height - it found range and height was computed by the combination of radar (slant) range and optical angle of sight.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by wmh829386 »

It is extremely difficult to compare individual FC system based on operational performance reported by different navies. Especially because RN and USN have difference attitude towards kill counts (I believe you have stress that in previous posts.) Hence it is almost impossible to proof or disproof anything about individual FC system from combat reports. The best could be deduced is only the overall effectiveness with all systems and operational factors combined.

(An analogy would be to attack the Dreyer's Table based on the performance of BCF's shooting... that is another deep deep rabbit hole. But in that case, put a long story short, it was revealed that the BCF gun crews are far below standard during the action. (and even that claim could be controversial) I doubt any individual AA action in WW2 could receive the scrutiny and wealth of gun data like the Jutland does with the added issue of medium & short range AA and CAP in the mix, hence almost nothing could be proven for the LA AA alone.)

I can concede that Mk 37/ Mk1 (along with the limited short range AA) was not effective enough to stop the strikes from IJN TB and DB getting through in 1942 and even 1943. But the point is almost moot when FC channels are always saturated in coordinated attacks. It is then justified to claim that a single elaborate LA AA director is far less important than giving multiple short/medium range FC to a ship, which is what was done later. However, it does not mean HACS and Mk37/Mk1 are equally ineffective, and the case of HACS being less effective is quite strong.

The problem with the HACS is that the core of the system (HACT deflection screen and assumption of constant height) is not accurate enough to take advantage of radar and VT fuse, while Mk37/Mk1 was quite successful. I can't dig up all the sources (shame!) at the moment but I rely on three main evidences.

1. The report by officers in pre-war exercise that setup that brings burst on target often does not corresponds to observation of target sleeves.
2. Report that VT fuse does not improve performance of DP AA
3. Description of principles of the HACS from the Gunnery Pocket Book

The first two are pretty self-evident and Friedman's book on Naval Anti-aircraft gunnery is one place to look for them. The third point need a little bit of explanation and it is quite technical. I should first make a disclaimer; some authors introduced the idea of "tachymetric" FC system and how it is superior, I find that distinction pointless as FC system follows a trend of taking more data and leave less to spotting correction anyway. No mention of that idea will be made.

Six numbers are required to represent the velocity and position of a plane. In the case of Mk37/Mk1 it uses bearing from ship, range, height, plane heading, speed, and rate of height change. (Other choices, like in “Flyplane”, are possible) The point is, HACS assumes the rate of height change is zero. And further assumes that the heading of the plane can be approximate by aligning graduation on a telescope to the fuselage, hence ignoring the effect of wind entirely even before ballistic calculation.

Multiple issues stem from the approach of HACS. First, if there is wind, the plane heading does not align with the length of its fuselage. Second, if the target is climbing or diving, the fuse timing and the amount of lead will both be wrong. Finally, for diving and climbing targets, because of the assumption and how HACT is integrated, correcting the amount of lead by playing with the speed estimate will just bring the fuse timing off and vice versa, unless the height setting is changed. But the height is calculated from the sight elevation and range finder (radar) to the table, so it cannot be “adjusted” like speed and inclination.

With regards to the claim that diving and climbing targets are always accelerating hence cannot be dealt by Mk37/Mk1 system. Although technically true, in the case of Mk37/Mk1, velocity of the target will be updated as the director tracks the target. Even though any solution will be outdated immediately, when compared with the HACS, Mk37/Mk1 will produce a closer firing solution and will be quicker to hit the target when target stop weaving.

For the type 285, I should be a bit clearer, it could get height estimate using max signal strength but it is not accurate enough for FC. Mk37 with its radar can lobe switch along vertical axis or horizontal axis, hence it can get accurate elevation, bearing and range on its own, hence can blind fire. Type 285 cannot. To be fair, I am not familiar with the various work-arounds for the HACS. I knew there are eyeshooting sights and GRUB. But I don’t see how they can overcome the inherent problem with the HACT.

Going back to the discussion of 4.5" vs 5"/38. The HACS is design to use in salvo fire, hence allowing spotting correction to be applied effectively. Hence the 4.5" with HACS can never develop the same volume of fire as 5"/38 with Mk37/Mk1 even though 4.5" with separate ammunition has similar max RoF.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by dunmunro »

wmh829386 wrote: Tue Oct 12, 2021 12:01 am 1) It is extremely difficult to compare individual FC system based on operational performance reported by different navies. Especially because RN and USN have difference attitude towards kill counts (I believe you have stress that in previous posts.) Hence it is almost impossible to proof or disproof anything about individual FC system from combat reports. The best could be deduced is only the overall effectiveness with all systems and operational factors combined.

(An analogy would be to attack the Dreyer's Table based on the performance of BCF's shooting... that is another deep deep rabbit hole. But in that case, put a long story short, it was revealed that the BCF gun crews are far below standard during the action. (and even that claim could be controversial) I doubt any individual AA action in WW2 could receive the scrutiny and wealth of gun data like the Jutland does with the added issue of medium & short range AA and CAP in the mix, hence almost nothing could be proven for the LA AA alone.)

2)I can concede that Mk 37/ Mk1 (along with the limited short range AA) was not effective enough to stop the strikes from IJN TB and DB getting through in 1942 and even 1943. But the point is almost moot when FC channels are always saturated in coordinated attacks. It is then justified to claim that a single elaborate LA AA director is far less important than giving multiple short/medium range FC to a ship, which is what was done later. However, it does not mean HACS and Mk37/Mk1 are equally ineffective, and the case of HACS being less effective is quite strong.

3)The problem with the HACS is that the core of the system (HACT deflection screen and assumption of constant height) is not accurate enough to take advantage of radar and VT fuse, while Mk37/Mk1 was quite successful. I can't dig up all the sources (shame!) at the moment but I rely on three main evidences.

1. The report by officers in pre-war exercise that setup that brings burst on target often does not corresponds to observation of target sleeves.
2. Report that VT fuse does not improve performance of DP AA
3. Description of principles of the HACS from the Gunnery Pocket Book

4)The first two are pretty self-evident and Friedman's book on Naval Anti-aircraft gunnery is one place to look for them. The third point need a little bit of explanation and it is quite technical. I should first make a disclaimer; some authors introduced the idea of "tachymetric" FC system and how it is superior, I find that distinction pointless as FC system follows a trend of taking more data and leave less to spotting correction anyway. No mention of that idea will be made.

5)Six numbers are required to represent the velocity and position of a plane. In the case of Mk37/Mk1 it uses bearing from ship, range, height, plane heading, speed, and rate of height change. (Other choices, like in “Flyplane”, are possible) The point is, HACS assumes the rate of height change is zero. And further assumes that the heading of the plane can be approximate by aligning graduation on a telescope to the fuselage, hence ignoring the effect of wind entirely even before ballistic calculation.

6)Multiple issues stem from the approach of HACS. First, if there is wind, the plane heading does not align with the length of its fuselage. Second, if the target is climbing or diving, the fuse timing and the amount of lead will both be wrong. Finally, for diving and climbing targets, because of the assumption and how HACT is integrated, correcting the amount of lead by playing with the speed estimate will just bring the fuse timing off and vice versa, unless the height setting is changed. But the height is calculated from the sight elevation and range finder (radar) to the table, so it cannot be “adjusted” like speed and inclination.

7)With regards to the claim that diving and climbing targets are always accelerating hence cannot be dealt by Mk37/Mk1 system. Although technically true, in the case of Mk37/Mk1, velocity of the target will be updated as the director tracks the target. Even though any solution will be outdated immediately, when compared with the HACS, Mk37/Mk1 will produce a closer firing solution and will be quicker to hit the target when target stop weaving.

8)For the type 285, I should be a bit clearer, it could get height estimate using max signal strength but it is not accurate enough for FC. Mk37 with its radar can lobe switch along vertical axis or horizontal axis, hence it can get accurate elevation, bearing and range on its own, hence can blind fire. Type 285 cannot. To be fair, I am not familiar with the various work-arounds for the HACS. I knew there are eyeshooting sights and GRUB. But I don’t see how they can overcome the inherent problem with the HACT.

9)Going back to the discussion of 4.5" vs 5"/38. The HACS is design to use in salvo fire, hence allowing spotting correction to be applied effectively. Hence the 4.5" with HACS can never develop the same volume of fire as 5"/38 with Mk37/Mk1 even though 4.5" with separate ammunition has similar max RoF.
1)Actually, it's not that difficult if we use postwar analysis by authors such as Lundstrom, Shores and Cull, who carefully compared both sides claims versus actual losses and were able to use the combat reports to assign a probable cause for each aircraft downed. When we do this we can see that RN and USN AA FC performed more alike than not.

2) Post war analysis proves that against level bombers, HACS seems to have performed somewhat better than MK33/37 and even at Midway where the number of IJNAF strikes was small 5in AA was almost a non factor. Lundtrom's assessment was that AA only downed 10 IJNAF aircraft in the carrier TF AA battles at Coral Sea, Midway, and Eastern Solomons versus about 90 award AA kills, and Lundstrom credits the close range AA as getting most of the kills. At Eastern Solomons the USN BuOrd awarded 30 AA kills against 27 IJN strike sorties despite the fact that CAP fighters made numerous kill claims as well. The myth of MK33/37 derived from these these inflated BuOrd AA kill awards, which could not be effectively challenged in wartime and there was no attempt to do so until Lundstrom published his two Volume 'First Team' books on the naval airwar in the Pacific in 1942. OTOH, the RN was far more conservative in awarding AA kills and their wartime assessments were far closer to the truth as Shores and Cull show in their analysis. Unfortunately even authors such as Friedman haven't bother to consult these obvious sources of data, preferring instead to use BuOrd's grossly inflated kill awards.

3) Prewar RN AA drone trials were carefully recorded via phototriangulation and they seem to compare quite well to similar USN drone trials. The RN made it as difficult as possible to bring down target drones and used special low power bursters in their AA shells, and carefully restricted the number of guns per ship allowed to fire at the target, with only one ship allowed to fire on a target at a time.
1) HACS used feedback from observations to continuously correct the FC solution and the addition of radar ranging greatly improved the accuracy of prediction.
2) This isn't correct
3) ?

4) see last sentence of 2 and 3.

5) MK33/37 required the exact same initial inputs as HACS, except they didn't have HACS' optical aids to help them assess target direction. HACS continuously calculated target altitude and used the updated altitude for each FC prediction cycle. Prior to radar MK33/37's range data wasn't sufficiently accurate to allow for introducing target altitude change into the solution and they typically omitted this during target practise. The HADT's CO binocular graticule was used to provide an initial assessment of target course and this was then updated based upon observed target motion to establish a feedback loop and MK33/37 did the same except that they had no optical aid to help calculate the initial inputs. In 1940 the RN began using the Gyro Rate Unit (GRU) and it's computer (GRUB) to provide fully tachymetric data to the HACT and they began to introduce AA FC radars.

6) These issues were common to all AA FC systems. In practise the HACS feedback loop compensated for wind and winds aloft were seldom the same as wind at sea level, so introducing a wind correction was just as likely to harm the FC solution as aid it. Target changes in altitude and range could be predicted by feeding a false altitude and range into the HACT but generally, if the target was changing altitude rapidly it was better to switch to barrage fire aimed by the HADT CO's direct shooting sights. MK33/37 had much the same issues.

7) In practise Mk33/37 couldn't deal with diving targets.

8) MK33/37 didn't begin using MK4 FD radar until mid 1942. There was no inherent reason that HACS couldn't have used FD radar to provide blind fire as it could use all the same data, so this isn't a limitation of HACS, but rather that of the radar provided to it. However, the lighter weight of the HACS HADT and Type 285 radar meant that the weight saved could be used for other purposes such a providing more close range weapons, which ultimately killed the greatest number of aircraft anyways. Basically only low flying torpedo bombers posed a threat to ships at night. RN radar was sufficient to detect if the target was flying low enough to be making a torpedo attack and then radar was used to provide range and bearing (via type 285 lobe switching), with the gun elevation locked at low angles at the probable height of a TB attack. Type 282 radar was used to track AA targets for the close range armament and Type 283 for the main armament, via dedicated AA FC directors and the ABU AA FC computer. Obviously, even at night some aircraft could be detected optically and then the optical angle of sight could be combined with a radar range to provide accurate target height, course, range, bearing and range rate. During daylight targets flying below the HACT elevation limits (about 9 degrees) would be tracked via the eyeshooting sights and the guns fired at precalculated fuze settings for target speed, range and height according to a lookup table.

9) HACS carefully managed deadtime (time between loading the guns and firing them) and added the same DT to the fuze setting for each salvo fired, so that each shell in the salvo had exactly the same fuze setting. This ensured that each salvo produced the maximum lethal effect when the shells burst. OTOH, MK37 had no control over deadtime as the fuze setter ran continuously during the prediction cycle. Thus, as no gun was loaded at the same instant, every shell fired either continuously or via salvo fire, had a different fuze setting and thus the density of each burst pattern was considerably less than for an HACS fired salvo.
Last edited by dunmunro on Tue Oct 12, 2021 5:27 am, edited 1 time in total.
Byron Angel
Senior Member
Posts: 1655
Joined: Sun Mar 06, 2011 1:06 am

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by Byron Angel »

"7) In practise Mk33/37 couldn't deal with diving targets."


See OD3147 Navy Department, Bureau of Ordnance
“Defense against Dive-Bombers using Gun Directors Mk. XIX, Mk XXVIII, Mk XXXIII, and Mk.XXXVII.”
14 September 1939

Pages 9/10

Quote -

( c ) GUN DIRECTOR MK. XXXVII with COMPUTER MK. I
Within the limiting speeds given in the table on the following page, this director system will operate against a dive attack exactly the same as against any normal air target. In this condition the problem should be rate-controlled, then will automatically be compensated for all movements of the target away from the direct line of sight.

Dive Angle - - - - - Maximum Diving Speed (Knots)
90deg - - - - - - - - - - - - - 250
80deg - - - - - - - - - - - - - 254
70deg - - - - - - - - - - - - - 266
60deg - - - - - - - - - - - - - 289
50deg - - - - - - - - - - - - - 326
40deg - - - - - - - - - - - - - 389

- unquote


All earlier HA Gun Directors (Mk19, Mk28 and Mk33) required disablement of specific mechanical system computing functions and substitution of ad hoc manual operator tracking inputs in the event of a dive-attack.

The Mk 33 and the Mk37, as I have attempted to explain to you previously, were completely different systems. There is a reason why the Gun Director Mk33 is specifically described as being controlled by the Range-Keeper Mk 10, while the Mk37 is specifically described as being controlled by the Computer Mk 1. They are two different systems controlled by two different “operating systems”.


Byron
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by dunmunro »

Byron Angel wrote: Tue Oct 12, 2021 7:17 pm "7) In practise Mk33/37 couldn't deal with diving targets."


See OD3147 Navy Department, Bureau of Ordnance
“Defense against Dive-Bombers using Gun Directors Mk. XIX, Mk XXVIII, Mk XXXIII, and Mk.XXXVII.”
14 September 1939

Pages 9/10

Quote -

( c ) GUN DIRECTOR MK. XXXVII with COMPUTER MK. I
Within the limiting speeds given in the table on the following page, this director system will operate against a dive attack exactly the same as against any normal air target. In this condition the problem should be rate-controlled, then will automatically be compensated for all movements of the target away from the direct line of sight.

Dive Angle - - - - - Maximum Diving Speed (Knots)
90deg - - - - - - - - - - - - - 250
80deg - - - - - - - - - - - - - 254
70deg - - - - - - - - - - - - - 266
60deg - - - - - - - - - - - - - 289
50deg - - - - - - - - - - - - - 326
40deg - - - - - - - - - - - - - 389

- unquote


All earlier HA Gun Directors (Mk19, Mk28 and Mk33) required disablement of specific mechanical system computing functions and substitution of ad hoc manual operator tracking inputs in the event of a dive-attack.

The Mk 33 and the Mk37, as I have attempted to explain to you previously, were completely different systems. There is a reason why the Gun Director Mk33 is specifically described as being controlled by the Range-Keeper Mk 10, while the Mk37 is specifically described as being controlled by the Computer Mk 1. They are two different systems controlled by two different “operating systems”.


Byron
I have explained to you that I visited the USN Naval Historical Centre and obtained handbooks and schematics for the Mk33 and 37 and they are based upon essentially the same Ford computer with only minor variations in internal design and operation which is what the BuOrd official history by Rowland and Boyd states. However, regardless, operational analysis shows that "in practise Mk33/37 couldn't deal with diving targets." As I explained, the time to set up the FC solution into the computer and the difficulty in tracking the target optically and/or via radar meant that the probability of success was vanishingly small. In many cases, according to their action reports, the USN reverted to barrage fire against diving targets, just as per HACS.

Problems with the MK1 computer when faced with dive bomber attack:

https://maritime.org/doc/computermk1/pg380.htm

As an aside this is what the official internal administrative history of BuOrd states about the MK37 when first fitted with radar in Sept 1941:
"... relatively faster
solution times, and more facile operation through
improved housing for personnel, resulted in efficiency
in the wide variety of continuously changing War
situations. This effectiveness was not attained
without encountering difficulties. The most signifi-
cant in terms of development trend was that the
director-computer combination represented a previous-
1y untried closed-circuit servo loop, the inherent
instability of which was additionally exposed to
perturbations from ships' compass inputs, and more
disastrously at the guns, by the response character
istics of the latter's servos. When the first
complete director-to-gun system was tested, operation
was entirely unsatisfactory. This was a shipboard
installation, and the motions of the ship undoubtedly
contributed to difficulties. But the faults were
multiplied by the fact that the test was not with
an experimental model, but with equipment under
production for a large group of destroyers rapidly
approaching completion. The value, thus emphasized,
of an adequate test program for any basically new
development for combat use should not be forgotten..."
Some issues with the MK 4 FD radar (from Rowland and Boyd):
While no ideal or complete solution to the varied problems was
produced during the war, considerable progress was made. Control
of 5-inch guns against aircraft was the first objective of the
program, and the Bell Telephone Laboratories were given the job
of modifying the Mark 3 for that purpose. To the functions of the
Mark 3 the derivation of elevation angle was added; lobe switching
in elevation, the same technique used to give the Mark 3 its accuracy
in azimuth, proved the answer. Except for a new antenna and
an additional indicator for the pointer, the new model, designated
the Radar Equipment Mark 4, was essentially the same as the
Mark 3. Late in September 1941, the first installation was made
in the destroyer Roe. Before the end of the year production
models were available for installation.
The new equipment, while far from perfect, proved both versatile
and effective. Over 600 were installed before production was
finally stopped in the spring of 1944. The Mark 4 was generally
installed on the double-purpose battery directors of battleships,
cruisers, and destroyers. Even at the end of the war, after many of
the equipments had been replaced by more modern types and others
had been lost in battle, over 300 Mark 4's remained in service.
This was the equipment that won its reputation aboard the South
Dakota when on October 16, 1942, the battleship shot down 38
of 38 attacking planes.
Surface craft, too, suffered from the equipment's
effectiveness since it was controlling large double-purpose
guns. In some respects the device was more efficient for surface
than for antiaircraft work; one of its principal deficiencies was
that it could not give accurate elevation data on planes that
approached the ship at an angle of less than about 10°. Other fleet
criticisms of the Mark 4 were directed at the unsatisfactory "pip"
presentations on the elevation and train indicators, resulting in
operator fatigue, and at its only moderate tracking accuracy.
Successive modifications effected improvement, but ordnance
designers were meanwhile developing its successor, the Radar
Equipment Mark 12.
By late 1942 the new design had superseded the old, but production
problems delayed service use of the Mark 12 until mid-1944.
Deliveries scheduled for May 1943, for instance, were not actually
ready for shipboard installation until early 1944. Once the sets
were available in quantity, however, the production of the Mark 4
equipments was halted altogether. Its replacement, operating
on a higher frequency, eliminated most of the minor defects, but
still contained two major defects: an inability to track low angle
targets and insufficient resolution in the presence of multiple targets.
Time limitations meant that the Marks 4 and 12 were the
only radars to see wartime service for their particular functions,
but later developments running into the postwar period promised
the elimination of the remaining defects in the existing systems.
The outstanding weakness of the Marks 4 and 12—failure to
detect low flying targets—was met by a high priority development
that produced the Radar Equipment Mark 22. A supplement
rather than a replacement for the Marks 4 and 12, this equipment
was designed to permit low angle elevation determination. Produced
on a crash basis, the new model contained features which
were significant for the future progress in antiaircraft radar for
control of large guns. Operating on a higher frequency than its
predecessors, the Mark 22 provided a fan-shaped beam for scanning
in the vertical instead of the horizontal plane. The combination
of a rapid scan and a narrow, 1° beam provided adequate
elevation data on attacking planes all the way down to the horizon.
The haste with which the Mark 22 was pushed through resulted in
unsatisfactory packaging, but it nonetheless pointed the way
toward the solution of some of the outstanding problems for
antiaircraft fire control radar.
Note how BuOrd's over awarding kills, rather than critically and realistically conducting operational analysis (as was done in the RN) colours even this account. South Dakota was awarded 26 AA kills at Santa Cruz by BuOrd and her captain estimated that only 5% were via 5in fire. Lundstrom's analysis suggests that she downed something like 4-6 aircraft.
Last edited by dunmunro on Tue Oct 12, 2021 8:43 pm, edited 2 times in total.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by wmh829386 »

dunmunro wrote: Tue Oct 12, 2021 5:03 am
wmh829386 wrote: Tue Oct 12, 2021 12:01 am 1) It is extremely difficult to compare individual FC system based on operational performance reported by different navies. Especially because RN and USN have difference attitude towards kill counts (I believe you have stress that in previous posts.) Hence it is almost impossible to proof or disproof anything about individual FC system from combat reports. The best could be deduced is only the overall effectiveness with all systems and operational factors combined.

(An analogy would be to attack the Dreyer's Table based on the performance of BCF's shooting... that is another deep deep rabbit hole. But in that case, put a long story short, it was revealed that the BCF gun crews are far below standard during the action. (and even that claim could be controversial) I doubt any individual AA action in WW2 could receive the scrutiny and wealth of gun data like the Jutland does with the added issue of medium & short range AA and CAP in the mix, hence almost nothing could be proven for the LA AA alone.)

2)I can concede that Mk 37/ Mk1 (along with the limited short range AA) was not effective enough to stop the strikes from IJN TB and DB getting through in 1942 and even 1943. But the point is almost moot when FC channels are always saturated in coordinated attacks. It is then justified to claim that a single elaborate LA AA director is far less important than giving multiple short/medium range FC to a ship, which is what was done later. However, it does not mean HACS and Mk37/Mk1 are equally ineffective, and the case of HACS being less effective is quite strong.

3)The problem with the HACS is that the core of the system (HACT deflection screen and assumption of constant height) is not accurate enough to take advantage of radar and VT fuse, while Mk37/Mk1 was quite successful. I can't dig up all the sources (shame!) at the moment but I rely on three main evidences.

1. The report by officers in pre-war exercise that setup that brings burst on target often does not corresponds to observation of target sleeves.
2. Report that VT fuse does not improve performance of DP AA
3. Description of principles of the HACS from the Gunnery Pocket Book

4)The first two are pretty self-evident and Friedman's book on Naval Anti-aircraft gunnery is one place to look for them. The third point need a little bit of explanation and it is quite technical. I should first make a disclaimer; some authors introduced the idea of "tachymetric" FC system and how it is superior, I find that distinction pointless as FC system follows a trend of taking more data and leave less to spotting correction anyway. No mention of that idea will be made.

5)Six numbers are required to represent the velocity and position of a plane. In the case of Mk37/Mk1 it uses bearing from ship, range, height, plane heading, speed, and rate of height change. (Other choices, like in “Flyplane”, are possible) The point is, HACS assumes the rate of height change is zero. And further assumes that the heading of the plane can be approximate by aligning graduation on a telescope to the fuselage, hence ignoring the effect of wind entirely even before ballistic calculation.

6)Multiple issues stem from the approach of HACS. First, if there is wind, the plane heading does not align with the length of its fuselage. Second, if the target is climbing or diving, the fuse timing and the amount of lead will both be wrong. Finally, for diving and climbing targets, because of the assumption and how HACT is integrated, correcting the amount of lead by playing with the speed estimate will just bring the fuse timing off and vice versa, unless the height setting is changed. But the height is calculated from the sight elevation and range finder (radar) to the table, so it cannot be “adjusted” like speed and inclination.

7)With regards to the claim that diving and climbing targets are always accelerating hence cannot be dealt by Mk37/Mk1 system. Although technically true, in the case of Mk37/Mk1, velocity of the target will be updated as the director tracks the target. Even though any solution will be outdated immediately, when compared with the HACS, Mk37/Mk1 will produce a closer firing solution and will be quicker to hit the target when target stop weaving.

8)For the type 285, I should be a bit clearer, it could get height estimate using max signal strength but it is not accurate enough for FC. Mk37 with its radar can lobe switch along vertical axis or horizontal axis, hence it can get accurate elevation, bearing and range on its own, hence can blind fire. Type 285 cannot. To be fair, I am not familiar with the various work-arounds for the HACS. I knew there are eyeshooting sights and GRUB. But I don’t see how they can overcome the inherent problem with the HACT.

9)Going back to the discussion of 4.5" vs 5"/38. The HACS is design to use in salvo fire, hence allowing spotting correction to be applied effectively. Hence the 4.5" with HACS can never develop the same volume of fire as 5"/38 with Mk37/Mk1 even though 4.5" with separate ammunition has similar max RoF.
1)Actually, it's not that difficult if we use postwar analysis by authors such as Lundstrom, Shores and Cull, who carefully compared both sides claims versus actual losses and were able to use the combat reports to assign a probable cause for each aircraft downed. When we do this we can see that RN and USN AA FC performed more alike than not.

2) Post war analysis proves that against level bombers, HACS seems to have performed somewhat better than MK33/37 and even at Midway where the number of IJNAF strikes was small 5in AA was almost a non factor. Lundtrom's assessment was that AA only downed 10 IJNAF aircraft in the carrier TF AA battles at Coral Sea, Midway, and Eastern Solomons versus about 90 award AA kills, and Lundstrom credits the close range AA as getting most of the kills. At Eastern Solomons the USN BuOrd awarded 30 AA kills against 27 IJN strike sorties despite the fact that CAP fighters made numerous kill claims as well. The myth of MK33/37 derived from these these inflated BuOrd AA kill awards, which could not be effectively challenged in wartime and there was no attempt to do so until Lundstrom published his two Volume 'First Team' books on the naval airwar in the Pacific in 1942. OTOH, the RN was far more conservative in awarding AA kills and their wartime assessments were far closer to the truth as Shores and Cull show in their analysis. Unfortunately even authors such as Friedman haven't bother to consult these obvious sources of data, preferring instead to use BuOrd's grossly inflated kill awards.

3) Prewar RN AA drone trials were carefully recorded via phototriangulation and they seem to compare quite well to similar USN drone trials. The RN made it as difficult as possible to bring down target drones and used special low power bursters in their AA shells, and carefully restricted the number of guns per ship allowed to fire at the target, with only one ship allowed to fire on a target at a time.
1) HACS used feedback from observations to continuously correct the FC solution and the addition of radar ranging greatly improved the accuracy of prediction.
2) This isn't correct
3) ?

4) see last sentence of 2 and 3.

5) MK33/37 required the exact same initial inputs as HACS, except they didn't have HACS' optical aids to help them assess target direction. HACS continuously calculated target altitude and used the updated altitude for each FC prediction cycle. Prior to radar MK33/37's range data wasn't sufficiently accurate to allow for introducing target altitude change into the solution and they typically omitted this during target practise. The HADT's CO binocular graticule was used to provide an initial assessment of target course and this was then updated based upon observed target motion to establish a feedback loop and MK33/37 did the same except that they had no optical aid to help calculate the initial inputs. In 1940 the RN began using the Gyro Rate Unit (GRU) and it's computer (GRUB) to provide fully tachymetric data to the HACT and they began to introduce AA FC radars.

6) These issues were common to all AA FC systems. In practise the HACS feedback loop compensated for wind and winds aloft were seldom the same as wind at sea level, so introducing a wind correction was just as likely to harm the FC solution as aid it. Target changes in altitude and range could be predicted by feeding a false altitude and range into the HACT but generally, if the target was changing altitude rapidly it was better to switch to barrage fire aimed by the HADT CO's direct shooting sights. MK33/37 had much the same issues.

7) In practise Mk33/37 couldn't deal with diving targets.

8) MK33/37 didn't begin using MK4 FD radar until mid 1942. There was no inherent reason that HACS couldn't have used FD radar to provide blind fire as it could use all the same data, so this isn't a limitation of HACS, but rather that of the radar provided to it. However, the lighter weight of the HACS HADT and Type 285 radar meant that the weight saved could be used for other purposes such a providing more close range weapons, which ultimately killed the greatest number of aircraft anyways. Basically only low flying torpedo bombers posed a threat to ships at night. RN radar was sufficient to detect if the target was flying low enough to be making a torpedo attack and then radar was used to provide range and bearing (via type 285 lobe switching), with the gun elevation locked at low angles at the probable height of a TB attack. Type 282 radar was used to track AA targets for the close range armament and Type 283 for the main armament, via dedicated AA FC directors and the ABU AA FC computer. Obviously, even at night some aircraft could be detected optically and then the optical angle of sight could be combined with a radar range to provide accurate target height, course, range, bearing and range rate. During daylight targets flying below the HACT elevation limits (about 9 degrees) would be tracked via the eyeshooting sights and the guns fired at precalculated fuze settings for target speed, range and height according to a lookup table.

9) HACS carefully managed deadtime (time between loading the guns and firing them) and added the same DT to the fuze setting for each salvo fired, so that each shell in the salvo had exactly the same fuze setting. This ensured that each salvo produced the maximum lethal effect when the shells burst. OTOH, MK37 had no control over deadtime as the fuze setter ran continuously during the prediction cycle. Thus, as no gun was loaded at the same instant, every shell fired either continuously or via salvo fire, had a different fuze setting and thus the density of each burst pattern was considerably less than for an HACS fired salvo.
I am aware of the analysis done by Lundstrom and others. My point is that there is no way to determine why a particular FC system perform well or not even in after such analysis because the effectiveness also depends on crew training and tactical situation, but the actual gun data can never be found, so no analysis of the actual gun engagement cannot be drawn. Unlike say for Jutland Brooks can pull the signal log, recreate the tactical plot and the actual range plot/table from archive and pinpoint what went wrong.

I think made my point very clear that even the Mk37/Mk1 cannot stop a squadron of bomber that knows what it is doing and the situation you stated justify that idea. For your claim that "HACS seems to have performed somewhat better", can you show that the crews in your comparison aren't making mistakes, or that the lack of Air defense coordination of USN TF isn't the reason for any poor performance? What I am saying is that I equally distrust the argument of "Mk37/Mk1 seems to have performed better" base of some engagement results.

Let me put that very bluntly, the optical aid in the form if binocular graticule is not as useful as you made it out to be. It can be misleading when target is changing height or when wind it significant. Try observing passenger aircraft approaching airports nearby on a day that is not calm, the path of the plane will differ from the heading of its nose visibly by the naked eye. By late 1942, air search/warning radar would be a much better source of initial target heading anyway. Furthermore, the density of burst count or less if the solution generated by the FC is inaccurate. It might be more effective for applying spotting correction, but the density of burst from HACS managing deadtime need to be balanced with the much higher instantaneous RoF by Mk37/Mk1 with 5"/38.

On GRUB, do you have information of how HACT deal with rate of change in height if the input data from radar and GRUB suggested so? As far as I know, HACT does not predict change in height in any form, hence even if you put a Mk4 radar on HACS, it still cannot produce a correct firing solution on a heavy bomber on a stable "dive" of say 8 degree, it is not a problem for Mk37/Mk1. Can we at least agree that with VT fuse and Radar, Mk37/Mk1 with Mk4 radar is better than HACS with it mkIV director and Type 285 radar?

It is interesting to know about how RN plans to deal with night torpedo attack, because, correct me if I am wrong, the attacking profile of the Swordfish would have dunk that plan by diving late to attack altitude to minimize time expose to AA fire (and basically skip the heavy AA lock to low. altitude entirely) on the other hand Mk37/Mk1 with Mk4 radar could blind fire and shoot down swordfish when the strike group is tracking with its ASV radar and not maneuvering much.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by wmh829386 »

I am aware of the analysis done by Lundstrom and others. My point is that there is no way to determine why a particular FC system perform well or not even after such analysis because the effectiveness also depends on crew training and tactical situation. Since the actual gun data is not available, analysis of the actual gun engagement cannot be drawn. Unlike say for Jutland Brooks can pull the signal log, recreate the tactical plot and the actual range plot/table from archive and pinpoint what went wrong.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by dunmunro »

wmh829386 wrote: Tue Oct 12, 2021 11:36 pm I am aware of the analysis done by Lundstrom and others. My point is that there is no way to determine why a particular FC system perform well or not even after such analysis because the effectiveness also depends on crew training and tactical situation. Since the actual gun data is not available, analysis of the actual gun engagement cannot be drawn. Unlike say for Jutland Brooks can pull the signal log, recreate the tactical plot and the actual range plot/table from archive and pinpoint what went wrong.
I have read almost all of the USN action reports for each ship present in the major naval surface to air battles during WW2. The plain and simple fact is that Mk33/37 didn't perform well and seems to have been no better than HACS, at least in 1942.
dunmunro
Senior Member
Posts: 4394
Joined: Sat Oct 22, 2005 1:25 am
Location: Langley BC Canada

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by dunmunro »

wmh829386 wrote: Tue Oct 12, 2021 11:30 pm [

1)I am aware of the analysis done by Lundstrom and others. My point is that there is no way to determine why a particular FC system perform well or not even in after such analysis because the effectiveness also depends on crew training and tactical situation, but the actual gun data can never be found, so no analysis of the actual gun engagement cannot be drawn. Unlike say for Jutland Brooks can pull the signal log, recreate the tactical plot and the actual range plot/table from archive and pinpoint what went wrong.

2) I think made my point very clear that even the Mk37/Mk1 cannot stop a squadron of bomber that knows what it is doing and the situation you stated justify that idea. For your claim that "HACS seems to have performed somewhat better", can you show that the crews in your comparison aren't making mistakes, or that the lack of Air defense coordination of USN TF isn't the reason for any poor performance? What I am saying is that I equally distrust the argument of "Mk37/Mk1 seems to have performed better" base of some engagement results.

3) Let me put that very bluntly, the optical aid in the form if binocular graticule is not as useful as you made it out to be. It can be misleading when target is changing height or when wind it significant. Try observing passenger aircraft approaching airports nearby on a day that is not calm, the path of the plane will differ from the heading of its nose visibly by the naked eye. By late 1942, air search/warning radar would be a much better source of initial target heading anyway. Furthermore, the density of burst count or less if the solution generated by the FC is inaccurate. It might be more effective for applying spotting correction, but the density of burst from HACS managing deadtime need to be balanced with the much higher instantaneous RoF by Mk37/Mk1 with 5"/38.

4) On GRUB, do you have information of how HACT deal with rate of change in height if the input data from radar and GRUB suggested so? As far as I know, HACT does not predict change in height in any form, hence even if you put a Mk4 radar on HACS, it still cannot produce a correct firing solution on a heavy bomber on a stable "dive" of say 8 degree, it is not a problem for Mk37/Mk1. Can we at least agree that with VT fuse and Radar, Mk37/Mk1 with Mk4 radar is better than HACS with it mkIV director and Type 285 radar?

5) It is interesting to know about how RN plans to deal with night torpedo attack, because, correct me if I am wrong, the attacking profile of the Swordfish would have dunk that plan by diving late to attack altitude to minimize time expose to AA fire (and basically skip the heavy AA lock to low. altitude entirely) on the other hand Mk37/Mk1 with Mk4 radar could blind fire and shoot down swordfish when the strike group is tracking with its ASV radar and not maneuvering much.
1) see next post.

2) I examined the performance of USN and RN ships, in the Pacific that underwent level bomber attacks and the reasons for the superior RN performance was probably due to their use of FC radar and the very poor performance of USN stereo rangefinders.

3) Again, HACS had an optical aid to assist the HADT's assessment of target course and MK37 didn't have that, yet both HACS and MK37 needed to input an estimated target course before opening fire. In 1942 the RN had AA FC radar which the USN didn't get until the mid part of that year, so HACS had better optical and radar methods of determining target course than Mk37. Of course the war started in 1939 and the RN began using AA FC radar in early 1940.

4) GRUB used the GRU data to predict the targets course and altitude change then fed the HACT data that the HACT could use to make accurate predictions of altitude change, (for example, by sending the HACT data anticipated range and elevation data) , as long as the altitude change was not extreme. If altitude change was extreme the best option was to use barrage fire via the CO's eyeshooting sights and this was true for Mk37 as well. I have pointed out that Mk4 FD radar was not accurate below 10deg elevation and so at night MK37 had no advantage against low flying aircraft, such as torpedo bombers. In daylight attacks against steeply diving aircraft (such as a kamikaze), MK37 had trouble with slow computer solutions and would often switch to the CO's eyeshooting sights or pass the gun to a Mk51 director. A directly approaching aircraft is actually a good target for eyeshooting with VT ammo since it's a low deflection shot.

5) Fortunately no other navy employed aircraft that could dive steeply during a TB attack. IJN/Axis doctrine was to come in low at night, where FD radar didn't work well, to underfly long range radar detection. Long range fire, even with radar and VT ammo was typically ineffective anyways.

Yes, on paper Mk37 had advantages but the fundamental problem was that it still had to predict based upon straight line target motion and in practise this resulted in almost the same level of effectiveness (or ineffectiveness) as HACS.
wmh829386
Member
Posts: 189
Joined: Mon Oct 04, 2021 5:43 pm

Re: British 4.5"/45 (11.4 cm) vs American 5"/38 (12.7 cm) Mark 12

Post by wmh829386 »

It is interesting that the preceived superiority of the HACS (this is a controversial point which I can set aside for now) is due to the radar. But it doesn't make HACS the better system.

Can you elaborate on the optical aid on the HACS? I am only aware of the the binocular gradticule and the strip field RF and sights receiving the output of HACT. If that's the only aids, than the inability for HACT to take in rate of change in height becomes a big problem that hinders the use of feedback.

Let say medium bomber comes in at 180kt, carrying a torpedo at 2500ft, flying straight and level. The HACS successfully tracks the target and fire is open. At this point the bomber make a shallow "dive" of 10~20 degrees to torpedo altitude (it can't just let the plane accelerate and arriving to fast at the drop off point). I think this attack profile is pretty feasible.

From the HACS, the taget will drift low show a lower bearing rate, the RF will drift out of coincidence. The quickest way to address the drift is to turn the binocular gradticule , but that is wrong as that would change the heading of the plane in the HACT. The correct solution is to essentially not do anyting (keeping the sights and RF on target manually) to the rates and use spotting correction lower the height of the burst. But that also means the feedback from the HACT is no longer useful, any further change of speed or course can't be told from the sigts drifting off.
In the Mk37, reducing the rate the target drifts off the current setting will bring the FC solution closer to reality, but in HACS, when every change in height happens, even for mild maneuver, the feedback falls apart.

For the GRUB, do you have a source on how height change is handled? Because in every account I have seen thus far, HACT only acceptes one height, so is it the current height is used or the future height which must be calculated from a sepertate intrument from current height, average projectile velocity, and target speed? Regardless of which value is used, the output from HACT cannot be used to track target that is changing height effectively.

For the point of Mk4 radar not being good for low flying aircraft, I doubt any axis aircraft could locate enemy fleet while itself is flying near the deck, furthermore it is a radar problem, let's say a mk37 has the type 285 instead, it would surely perform better than HACS using eyeshooting sight right?
Post Reply